[6.x] Handle download responses in Inertia requests

src/Http/Middleware/CP/HandleInertiaRequests.php

@@ -3,9 +3,13 @@
 namespace Statamic\Http\Middleware\CP;
 
 use Illuminate\Http\Request;
+use Inertia\Inertia;
 use Inertia\Middleware;
 use Statamic\CP\Toasts\Manager;
 use Statamic\Statamic;
+use Symfony\Component\HttpFoundation\BinaryFileResponse;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpFoundation\StreamedResponse;
 
 use function Statamic\trans as __;
 
@@ -38,6 +42,15 @@ public function share(Request $request): array
         ]);
     }
 
+    public function onEmptyResponse(Request $request, Response $response): Response
+    {
+        if ($response instanceof StreamedResponse || $response instanceof BinaryFileResponse) {
+            return Inertia::location($request->fullUrl());
+        }
+
+        return parent::onEmptyResponse($request, $response);
+    }
+
     private function logos()
     {
         if (! Statamic::pro()) {

tests/Http/Middleware/HandleInertiaRequestsTest.php

@@ -0,0 +1,78 @@
+<?php
+
+namespace Tests\Http\Middleware;
+
+use Illuminate\Support\Facades\Route;
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Facades\User;
+use Statamic\Statamic;
+use Tests\PreventSavingStacheItemsToDisk;
+use Tests\TestCase;
+
+class HandleInertiaRequestsTest extends TestCase
+{
+    use PreventSavingStacheItemsToDisk;
+
+    protected function resolveApplicationConfiguration($app)
+    {
+        parent::resolveApplicationConfiguration($app);
+
+        Statamic::pushCpRoutes(function () {
+            Route::get('streamed-download-test', function () {
+                return response()->streamDownload(fn () => print 'id,name', 'data.csv');
+            });
+
+            Route::get('file-download-test', function () {
+                return response()->download(__FILE__);
+            });
+
+            Route::get('empty-response-test', function () {
+                return response()->noContent(200);
+            });
+        });
+    }
+
+    #[Test]
+    public function it_converts_streamed_downloads_into_location_visits_for_inertia_requests()
+    {
+        // Inertia requests are made over XHR, which can't trigger downloads. Returning
+        // 409 + X-Inertia-Location makes the client do a full browser visit instead,
+        // which lets the browser handle the download natively.
+
+        $this
+            ->actingAs(User::make()->makeSuper())
+            ->get('/cp/streamed-download-test', ['X-Inertia' => 'true'])
+            ->assertStatus(409)
+            ->assertHeader('X-Inertia-Location', 'http://localhost/cp/streamed-download-test');
+    }
+
+    #[Test]
+    public function it_converts_file_downloads_into_location_visits_for_inertia_requests()
+    {
+        $this
+            ->actingAs(User::make()->makeSuper())
+            ->get('/cp/file-download-test', ['X-Inertia' => 'true'])
+            ->assertStatus(409)
+            ->assertHeader('X-Inertia-Location', 'http://localhost/cp/file-download-test');
+    }
+
+    #[Test]
+    public function it_leaves_downloads_untouched_for_non_inertia_requests()
+    {
+        $this
+            ->actingAs(User::make()->makeSuper())
+            ->get('/cp/streamed-download-test')
+            ->assertOk()
+            ->assertDownload('data.csv');
+    }
+
+    #[Test]
+    public function it_redirects_back_for_empty_inertia_responses()
+    {
+        $this
+            ->actingAs(User::make()->makeSuper())
+            ->from('/cp/utilities')
+            ->get('/cp/empty-response-test', ['X-Inertia' => 'true'])
+            ->assertRedirect('/cp/utilities');
+    }
+}